S cams are widely used in the commercial trucking industry. The S cam is an intermediary device between a pneumatic brake actuator and a set of wheel brakes. The S cam is typically an elongate metal rod or shank having an S-head at one end and a set of splines at the other end. Each of the individual arms of the S-head engages a respective brake shoe. Rotation of the S cam causes the arms of the S-head to bear on the respective brake shoe, causing the brake shoe to frictionally engage the brake drum that is affixed to the wheel. In the past, the S cam has been rotationally supported by at least two bushings. A first bushing was positioned proximate the S-head and a second bushing was positioned proximate the splines.
The bushings have typically been exposed to the elements as the S cam is mounted exposed rearward of the axle of the vehicle. The intrusion of water, salt, and dirt into each of the bushings causes the bushings to fail in relatively short order. Replacement of the bushings is a necessarily frequent task that keeps the vehicle off the road for a significant period of time.
More recently, a Canadian company has provided a single tube that substantially encloses the elongate shank of the S cam and the two bushings.
There is a need in the industry to reduce the number of bushings that support the S cam and to provide for a longer service life of such bushing.